Within the integrated circuit industry there is a continuing effort to increase integrated circuit speed as well as device density. As a result of these efforts, there is a trend towards using flip chip technology when packaging complex high speed integrated circuits. Flip chip technology is also known as control collapse chip connection (C4) technology. In C4 technology, the integrated circuit die is flipped upside down. This is opposite to how integrated circuits are typically packaged today using wire bond technology. By flipping the integrated circuit die upside down, ball bonds may be used to provide direct electrical connections between the die and the package. Unlike wire bond technology, which only allows bonding along the periphery of the integrated circuit die, C4 technology allows connections to be placed anywhere on the integrated circuit die surface. This leads to a very low inductance power distribution to the integrated circuit which is another major advantage of C4 technology.
As integrated circuit technology has improved, substantially greater functionality has been incorporated into the devices. As integrated circuits have expanded in functionality, the size of the devices has diminished resulting in higher clocking frequencies and increased power consumption. As a consequence, the integrated circuit devices of today generate more heat while possessing smaller surface areas to dissipate the heat. Therefore, it is important to have a high rate of heat transfer from the integrated circuit package to maintain the junction temperatures of the integrated circuit within safe operating limits. Excessive junction temperatures may affect the performance of the circuit and cause permanent degradation of the chip.
Conventional packages typically use cooling plates to spread the heat generated by a semiconductor device and to transfer the heat to an external heat sink. Spreading the heat generated by the semiconductor device serves to reduce the heat flux at the package surface. By reducing the heat flux at the package surface, heat can be more efficiently removed by an external heat sink. The cooling plates or heat spreaders, as they are commonly called, are generally made of a thin metal plate, such as copper or aluminum. Although the use of cooling plates has proved sufficient in the past, they are unable to adequately reduce the heat flux at the surface of many present day packages that house high power generating components.
Therefore, what is needed is an apparatus for reducing the heat flux at the surface of high power semiconductor packages.